A constructed Holliday junction was examined in the STEM. It was composed of RuvA, RuvB, and a crossover DNA, in a ATP-y-S, Mg++ reaction mixture. The double-stranded DNA 11arms11 coming out of the complex were 660, 850, 1500, and 1940 base pairs in length. Two copies of RuvB rings (known to be hexamers of a 38 k')a protein) flank the RuvA in the center~ of the complex. The mass of the complex was measured to determine the number of copies of RuvA present.